The Ultimate Google Algorithm Cheat Sheet by Neil Patel.
From the post:
Have you ever wondered why Google keeps pumping out algorithm updates?
Do you understand what Google algorithm changes are all about?
No SEO or content marketer can accurately predict what any future update will look like. Even some Google employees don’t understand everything that’s happening with the web’s most dominant search engine.
All this confusion presents a problem for savvy site owners: Since there are about 200 Google ranking factors, which ones should you focus your attention on after each major Google algorithm update?
Google has issued four major algorithm updates, named (in chronological order) Panda, Penguin, Hummingbird and Pigeon. In between these major updates, Google engineers also made some algorithm tweaks that weren’t that heavily publicized, but still may have had an impact on your website’s rankings in search results.
…
A very detailed post describing the history of changes to the Google algorithm, the impact of those changes and suggestions for how you can improve your search rankings.
The post alone is worth your attention but so are the resources that Neil relies upon, such as:
200 Google ranking factors, which really is a list of 200 Google ranking factors.
I first saw this in a tweet by bloggerink.